Hydrocarbon separations



United States Patent 3,517,079 HYDROCARBON SEPARATIONS Rodney D. Beckham, Bridgeton, George D. Davis, Creve Coeur, and Earle C. Makin, Jr., St. Louis, Mo., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed July 29, 1968, Ser. No. 748,201 Int. Cl. C07c 7/10 US. Cl. 260-674 Claims ABSTRACT OF THE DISCLOSURE A process for the separation and recovery of vinyl aromatic hydrocarbons from admixture with alkyl aromatic hydrocarbons by means of selective complex formation using cuprous fiuoroborates or cuprous fluorophosphates as the complexing agent. Means for stabilizing cuprous fluoroborate and cuprous fluorophosphate complexing agents also are provided.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a process for the separation, purification and recovery of certain hydrocarbons. More particularly, the present invention relates to a process for the separation and recovery of vinyl aromatic hydrocarbons, i.e., styrene, vt-Illfithyl styrene, from alkyl aromatic hydrocarbons, i.e., xylenes, ethylbenzene, etc.

Prior art One of the most difficult separations problem existing in industry today is that of separating vinyl aromatic hydrocarbons from close boiling alkyl aromatic hydrocarbons. As used herein, the term vinyl aromatic hydrocarbons refers to aromatic hydrocarbons containing at least one mono-ethylenically unsaturated aliphatic substituent, i.e., styrene, a-methyl styrene, fi-methyl styrene, vinyl toluene, divinyl benzene, vinyl naphthalene, etc. The term alkyl aromatic hydrocarbons refers to those hydrocarbons having saturated aliphatic substituents, i.e., xylenes, ethylbenzenes, ethyl toluenes, ethyl naphthalene, etc. In most instances, the separation of vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons is difficult at best by distillation. To render the problem more difficult, the unsaturated vinyl aromatic hydrocarbons readily polymerize, particularly at temperatures required for distillation, and thereby significant quantities of these materials are lost and the resulting polymer fouls the distillation equipment. Probably, the most exemplary and commonly encountered difiicultly separable vinyl aromatic hydrocarbon and alkyl aromatic hydrocarbons are styrene and ethylbenzene and the close boiling xylenes, particularly ortho-xylene. These compounds are difficult to separate one from another and because of the entirely different uses to which the two compounds are put, either is an undesirable contaminant in the other.

As an alternative to distillation, such means as solvent extraction, extraction distillation, azeotropic distillation and complex formation have been investigated as a means for the separation of vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons. With respect to complex formation, it is known that such compounds as mercuric chloride, mercuric acetate, and the like will complex with styrene. However, the selectivity of these complexing agents for such vinyl aromatic hydrocarbons as styrene is not as great as desired. Further, it is generally quite difiicult to recover the vinyl aromatic hydrocarbons from the complex. Severe conditions are often necessary for recovering the complexed vinyl aromatic hydrocar- "ice bons and such conditions also result in significant polymerization and loss of the vinyl aromatic hydrocarbons.

Other complex forming agents such as certain copper fluoroborates and the silver fluoroborates and fluorosilicates are known to form complexes with aromatic hydrocarbons. However, these compounds are equally well known for their ability to complex with both alkyl aromatics and with vinyl aromatics. Up to the present, activity with respect to these complexing agent appears to have centered primarily around separation of aromatic hydrocarbons, as a class, from non-aromatic hydrocarbons, also as a class. Such separations are the subjects of US. Pats. Nos. 2,953,589 and 3,201,489. The known usage of these materials as complexing agents also sufiers the above discussed disadvantage of difficulty of recovery of the complexed aromatic hydrocarbons from the complex. It is an object of the present invention to provide a new and improved process for the separation of hydrocarbons. Particularly, it is an object of the present invention to provide a new and improved process for the separation of vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons. It is also an object of the present invention to provide a new and improved process for the separation of vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons wherein the vinyl aromatic hydrocarbons may be readily recovered. Yet, another object of the present invention is to provide a means whereby vinyl aromatic hydrocarbons and olefin hydrocarbons may be readily and simply recovered from certain complexes of which such hydrocarbons are a part. Another object of the present invention is to provide new and novel compositions useful in the separation of hydrocarbons. Additional objects will become apparent from the following description of the invention herein disclosed.

SUMMARY OF THE INVENTION The present invention, which fulfills these and other objects, is a process which provides for the separation and recovery of vinyl aromatic hydrocarbons from admixture with alkyl aromatic hydrocarbons, the process comprising contacting a mixture of said vinyl aromatic hydrocarbons and said alkyl aromatic hydrocarbons with a first complex which comprises a cuprous salt selected from the group consisting of cuprous fluoroborate and cuprous fluorophosphate and a hydrocarbon selected from the group consisting of olefins, aromatic hydrocarbons and mixtures of olefins and aromatic hydrocarbons, the aromatic hydrocarbons being other than vinyl aromatic hydrocarbons, thereby forming a first extract phase and a first raflinate phase, separating said first extract phase and said first raffinate phase, and recovering from said first extract phase a hydrocarbon fraction substantially richer in vinyl aromatic hydrocarbons than the original mixture. In the preferred practice of the present invention, the vinyl aromatic hydrocarbons are recovered from the first extract phase by contacting said first extract phase with olefin hydrocarbons in a molar amount at least substantially equal to the amount of vinyl aromatic hydrocarbons in said first extract phase, thereby forming a second extract and a second raflinate phase, and recovering a vinyl aromatic hydrocarbon fraction from said second rafiinate phase, said vinyl aromatic hydrocarbon fraction being substantially richer in vinyl aromatic hydrocarbons than the original mixture of vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons. The second extract phase obtained as a result of recovering vinyl aromatic hydrocarbons from the first extract phase by means of contacting the first extract phase with olefin hydrocarbons, can generally be used as the first complex for the separation of an additional mixture of vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons.

In carrying out the process of the present invention, it frequently is desirable to employ a noncomplexible hydrocarbon diluent or solvent as an aid to formation of the extract and raffinate phases and/ or for further extracting the extract phases formed in the present process to remove from such extract phase the alkyl aromatic hydrocarbons which are not complexed with the cuprous salt. For example, a noncomplexible hydrocarbon such as a lower molecular weight pariffin hydrocarbon, i.e., hexane, may be introduced into contact with the first complex concurrently with the mixture of vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons. The use of such a noncomplexible hydrocarbon diluent results in a more rapid phase formation as well as in more efiicient removal of noncomplexed feed materials from the extract phase to the raffinate phase thereby producing an extract phase richer in the complexible vinyl aromatic hydrocarbons than is obtained without the use of the noncomplexible diluent. The use of the noncomplexible hydrocarbon diluent or solvent as a further extractant of the extract merely comprises contacting the extract phase with the noncomplexible hydrocarbon solvent to thereby absorb in the solvent noncomplexed feed hydrocarbons which may be present in the extract phase. Care must be used in selecting the noncomplexible hydrocarbon solvent in order that this diluent or solvent not be one which is itself difficultly separable from components of the extract or rafiinate phases.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to further describe the present invention, particularly with respect to the preferred embodiments thereof, the following examples are presented.

Example I A cuprous fiuoroborate first complex was formed in the following manner: 63.5 grams of powdered metallic copper along with 137.5 grams of CuF -2H O were dispersed in 644 grams of toluene. Gaseous BP was then continuously introduced into the dispersed medium until all of the solids had solubilized. The reaction mass was maintained at a temperature of approximately 110 C. and continuously agitated throughout addition of the BE, with continuous removal of water enerated. The agitation was continued beyond the period of BF addition and the product then cooled back to ambient temperatures (73-75 F.). Approximately 85 grams of the resulting liquid cuprous fiuoroborate-toluene first complex was then stabilized by agitating at a temperature of C. in the presence of grams of butene-l and 48 grams of sulfolane. Two phases formed, a raffinate and an extract phase, and were separated. The extract phase was the stabilized first complex and consisted of 0.25 mole (14.03 grams) of butene-l, 0.20 mole (18.42 grams) of toluene, 0.34 mole (40.80 grams) of sulfolane and 0.20 mole (30.0 grams) of CuBF Example II To demonstrate the elficiency of the present invention in the separation of vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons, approximately 103.5 grams of the stabilized first complex prepared in Example I above was agitated with 42 grams of a 1:1, by weight, mixture of styrene and ethylbenzene. Temperature during the period of agitation was 25 C. After about 10 minutes, agitation was stopped and an extract and rafiinate phase allowed to form. The extract and rafiinate phases were then separated and each analyzed for ethylbenzene and styrene. The extract phase was found to contain approximately 579% by weight of the available styrene with the remainder being in the raffinate. The remaining portion of the extract phase was made up principally of the euprous fiuoroborate, sulfolane, toluene and butene-l with the remaining portion of the rafiinate phase being substantially all toluene and butane-1. The relative amounts of styrene and ethylbenzene in the extract and raifinate phases normalized to were as follows:

Component: styrene; extract, 78.4; raffinate, 32.1. Component: ethylbenzene; extract, 21.6; raifinate, 67.9.

The above results illustrate a change in the weight ratio of styrene to ethylbenzene from the 1:1 of the original mixture to approximately 3.511 in the extract and 0.47:1 in the raffinate.

To further concentrate the styrene in the extract, the above extract was washed with 37 grams of toluene. New extract and rafiinate phases formed and were separated. The mixture of styrene and ethylbenzene in the new extract phase was found to contain 89.8% by weight styrene and 10.2% by weight ethylbenzene for a weight ratio of styrene to ethylbenzene of approximately 8.811.

Example III To demonstrate the preferred mode of recovery of the vinyl aromatic fraction in accordance with the present invention, a portion of the final extract of Example 11 was contacted in a first stage with agitation and at a temperature of 0 C. with a mixture of toluene and 33.2% by weight of butene-l. The aromatic-olefin mixture was used in a weight ratio of approximately 0.52:1 to the final extract of Example II. The toluene was added to provide a liquid ralfinate phase into which the materials displaced from final extract phase of Example II by the butene-l would be absorbed. On stopping agitation, a raffinate and extract phase rapidly formed and were separated. The extract phase was found to contain 53.2% by weight of the available styrene and no detectable ethylbenzene. The ralfinate phase was found to contain 46.8% by weight of the available styrene in a weight ratio with the ethylbenzene of 7.92:1 as compared with the 1:1 weight ratio in the original mixture.

The extract phase was then contacted again in a second staeg under the same conditions as the first stage with the toluene-butenel mixture used in the first stage, the weight ratio of the aromatic-olefin mixture to the extract being 0.53:1. Again on stopping agitation, an extract and ratfinate phase quickly formed and were separated. The extract phase contained 57.1% by weight of the available styrene and no ethylbenzene. The raffinate phase was found to contain 42.9% by weight of the available styrene in a weight ratio of 20.1:1 to the ethylbenzene. By combination of the first and second stage raifinates, a styrene fraction containing approximately 69.6% by weight of the styrene available in the final extract of Example II is obtained. From this two-stage recovery, a styrene fraction containing styrene in a 9.5 :1 weight ratio to ethylbenzene is obtained as compared to the 1:1 ratio of ethylbenzene to styrene found in the original mixture.

Example IV To demonstrate the use, as the first complex, of the second extract obtained as a result of recovering vinyl aromatic hydrocarbons from the first extract by means of contacting the first extract with olefin hydrocarbons, the final extract phase of Example III which consisted of 33.5% CuBF 36.7% sulfolane, 2.4% styrene, 10.0% toluene and 17.4% butene-l, all percents by weight, was intimately contacted under the conditions of Example II with the 1:1 by weight styrene-ethylbenzene mixture used in Example II. The weight ratio of the extract phase of Example III to the styrene-ethylbenzene mixture was 0.47:1. On stopping agitation, an extract and raffinate phase formed and were separated and were analyzed for styrene and ethylbenzene. On analysis, the mixtures of styrene and ethylbenzene in the extract and raffinate phases were found to have the compositions presented below. The concentrations of styrene and ethylbenzene in the mixtures as presented below are normalized to 100%.

Component: styrene; extract, 73.2; raffinate, 30.8. Component: ethylbenzene; extract, 26.8; raffinate, 69.2.

Example V To demonstrate operation of the process of the present invention as a continuously operating process, a hydrocarbon mixture consisting of 48.2% by weight styrene and 51.8% by weight oxylene is continuously separated in an extraction column having approximately 24 perforated trays, each tray capable of operating at approximately 50% theoretical tray efficiency. A first complex is continuously introduced onto the top of the 24th tray (from bottom) of the extraction column. This first complex is one prepared as follows: Powdered metallic copper and CuF -2H O are dispersed in toluene, the weight ratio of Cu to CuF -2H O to toluene being 1:2.17:14.5. Gaseous BF is then passed through the mixture until it is completely in liquid phase. The reaction mass is maintained at a temperature of approximately 110 C. and continuously agitated throughout addition of the BF with continuous removal of the water generated. The agitation is continued for several minutes beyond the period of BF3 addition and the product cooled to ambient temperatures (73-75 F.). The mixture is then contacted with hexene-l in a weight ratio of 1:254, hexene-l to complex mixture thereby forming extract and rafiinate phases which are then separated. The extract phase is the first complex.

Concurrently with introduction of the first complex into the extraction column, the hydrocarbon feed mixture is introduced into the column between the 12th and 13th tray and n-heptane is introduced below the 1st tray. The column is operated at substantially ambient temperatures (7080 F.) and at autogenous pressure. The weight ratio of first complex to feed mixture to n-heptane is l: 1.3 10.62. A raffinate, termed the first raflinate, is continuously taken overhead from the extraction column and an extract, termed the first extract, is continuously taken from the bottom. The raffinate consists of about 28.1% by weight hexene-l, 37.6% by weight o-xylene, 3.4% by weight styrene, and 30.9% by weight n-heptane. The extract has the composition of 40.5% by weight CuBF 2.7% by weight heptane, 56.3% by weight styrene, and 0.5% by weight o xylene. The extract from the extraction column is continuously introduced into a second extraction column adjacent the top thereof. Hexene-l is continuousl introduced into the second extraction column adjacent the bottom thereof, the weight ratio of the extract from the first extraction column to the hexene-l being 1:1. This second extraction column is operated at substantially ambient temperatures of 70 to 80 F. and at autogenous pressures. A rafiinate, termed the second rafiinate, is continuously taken overhead from the second extraction column and an extract, termed the second extract, is continuously taken from the bottom. This second raffinate contains styrene, ortho-xylene, n-heptane and hexene-l. The weight ratio of styrene to ortho-xylene in this second raflinate is 92.75tl. The extract has the composition of 46.4% by weight CuBE; and 53.6% by weight hexene-l. The extract from this second extraction column is recycled back to the first extraction column as a part of the first complex.

The first raflinate phase is subjected to fractional distillation in a distillation column having approximately 30 trays, and a styrene-ortho-xylene fraction obtained which is substantially richer in ortho-xylene than was the original feed mixture to the first extraction column. The second raffinate is also subjected to fractional distillation in a column having approximately 30 trays. A styrene-orthoxylene fraction is obtained from this distillation which is substantially richer in styrene than was the original feed mixture to the first extraction column.

Example VI A cuprous fluorophosphate containing first complex was prepared as follows: about 68.8 grams of CuF -2H O and 37 grams of powdered metallic copper were dispersed in 460 grams of toluene with continuous agitation and at a temperature at to C. Phosphorus pentafluoride was introduced continuously until all solids were solubilized. To the resulting complex was added approximately 240 grams of sulfolane. On addition of the sulfolane, two phases formed and were separated. The extract phase represents the first complex. This first complex has the composition 31.2% by weight CuPF 39% by weight sulfolane and 29.8% by weight toluene.

A 1:1 by weight mixture of styrene and ortho-xylene is contacted at a temperature of approximately 25 C. and at autogenous pressure with the above-described cuprous fluorophosphate containing first complex in a weight ratio of complex to hydrocarbon of 0.5 1 1. Extract and raffinate phases form and are separated. A hydrocarbon fraction which is substantially richer in styrene than the original feed mixture is recovered from the extract phase while a hydrocarbon fraction substantially richer in ortho-xylene than the original feed mixture is recovered from the raffinate phase.

The cuprous salts employed in forming the complexes used in carrying out the process of the present invention are cuprous tetrafiuoroborate and cuprous hexafluorophosphate. Generally, these are referred to as cuprous fluoroborate and cuprous fluorophosphate. Both of these salts are relatively unstable and cannot be readily formed as the salt. As a result, the usual practice is to form the salt in the presence of an organic compound with which the salt will complex, thereby forming the salt and the complex of the salt with the organic compound almost concurrently.

The organic compounds in which the cuprous salts may be formed and with which such salts are immediately complexed may include any of a rather large number of such compounds. The choice of organic compound is often dictated by the hydrocarbons in the hydrocarbon mixture to be separated. Generally, however, the organic compounds will be aromatic hydrocarbons. Such aromatic hydrocarbons may contain a single aromatic ring or may contain two or more aromatic rings, either condensed or noncondensed. In addition, the aromatic hydrocarbons may have substituents to the ring or may be condensed with one or more other ring structures which are paraffinic or olefinic in nature. Nonlimiting examples of aromatic hydrocarbons suitable for use in preparing the cuprous salts of the present invention are benzene, toluene, the xylenes, various other polymethylbenzenes, such as mesitylene, isodurene, tri-, tetra-, pentaand hexamethylbenzenes, ethylbenzene and the various polyethylbenzenes, isopropylbenzenes, propylbenzene and the various polyisopropyland polypropylbenzenes, the various butyland pentylbenzenes and the like, the substituted benzenes containing two or more different substituents such as ethyltoluene, isopropyltoluene, and ethylxylenes; naphthalene, the various methylnaphthalenes, and polymethylnaphthalenes, ethylnaphthalene and the various polyethylnaphthalenes, the naphthalenes containing propyl, isopropyl, butyl, and pentyl substituents; the substituted naphthalenes containing two or more different substituents such as methylethylnaphthalene, methylpropylnaphthalenes, etc.; the various iudanes such as methylindanes, ethylindanes, isopropylindanes, etc.; the dihydronaphthalenes such as methyl, ethyl, propyl, and butyl substituted dihydronaphthalenes; the tetrahydronaphthalenes and the like. In the preferred practice of the present invention, the aromatic hydrocarbons most often employed as the organic compound in forming the complexes of the present invention are benzene, naphthalene, partially hydrogenated naphthalenes and the various alkyl substituted derivatives of these wherein the alkyl substituents have no more than four carbon atoms per substituent. Within this group of preferred aromatic hydrocarbons are such compounds as benzene, ethylbenzene, toluene, the xylenes, naphthalene and the methylnaphthalenes, dihydronaphthalenes and tetrahydronaphthalenes. A particularly useful group of aromatic hydrocarbons for use in forming the complexes is that including such compounds as toluene, ethylbenzene, ethyltoluene, the xylenes and tetrahydronaphthalene.

The method of preparing the cuprous fluoroboratearomatic hydrocarbon containing complex, referred to herein as the first complex, which is used for the separation of hydrocarbon mixtures in accordance with the present invention may be any of those methods conventionally used. In US. Pat. No. 2,953,589, the preparation of cuprous fluoroborate-aromatic hydrocarbon complexes by the introduction of powdered copper, BE; and anhydrous HF into benzene or other aromatic hydrocarbons is disclosed. This method may be used for the purposes of the present invention. In addition, the cuprous fiuoroborate-aromatic hydrocarbon complex may be prepared by dispersing CuF -ZH O and metallic copper in an aromatic hydrocarbon and heating the reaction mixture while introducing gaseous BF into the dispersed medium. This method is described in the Journal of the American Chemical Society, vol. 74, page 3702, 1952. This latter described method is preferred for the practice of the present invention. In addition to these two methods of preparing the cuprous fluoroborate-aromatic hydrocarbon complex, any other of the methods known to those skilled in the art may be used.

Preparation of the cuprous fiuorophosphate-aromatic hydrocarbon complex may be by any of those means known to those skilled in the art. Preferably, however, this complex is prepared by introducing anhydrous CuF or CuF -2H O metallic copper and phosphorus pentafluoride into an aromatic hydrocarbon medium and heating with agitation to an elevated temperature in excess of 75 C. The cuprous fluorophosphate-aromatic hydrocarbon complexes may on occasion be solid at room temperature and, therefore, must be maintained at elevated temperatures for use in the process of the present invention or, in the alternative, be used along with a suitable solvent. It is believed that impurities in the system cause these complexes to be solid. A number of solvents suitable for maintaining the cuprous fiuorophosphates in solution will be hereinafter discussed. In addition to the above method of preparing the cuprous fluorophosphatearomatic hydrocarbon complex, any other method known to the art may be used.

In preparing the cuprous salt-organic compound first complexes for use in the separations processes disclosed herein, some care should be exercised in the selection of the organic compound to avoid use of an organic compound which itself will be difficultly separable from hydrocarbons of the mixture to be separated. Each mole of the cuprous salt-organic compound first complexes formed in accordance with the present invention generally will contain at least two moles of organic compound and one mole of the cuprous salt. Separation of hydrocarbon mixtures in accordance with the processes disclosed herein, involves the displacement of one or more of the moles of organic compound from the first complex and substitution therein of at least one of the components of the hydrocarbon mixture to be separated. Since the organic compound displaced from the first complex by the complexible components of the mixture to be separated generally mixes freely with the components of the feed mixture which do not complex with the cuprous salt, the organic compound of the first complex should be one which is readily and simply separated from the noncomplexed hydrocarbons of the hydrocarbon mixture to be separated. To illustrate the above, if the hydrocarbon mixture to be separated is one comprised of styrene and ortho-xylene, it would not be desirable to use metaor para-xylenes or ethylbenzene as the organic compound in which the first complex is formed. If, for instance, para-xylene was used as the organic compound, the raffinateresulting from contact of the first complex with the mixture of styrene and ortho-xylene would contain a mixture of orthoand para-xylenes which compounds are difficultly separable from one another. If the mixture to be separated is one comprised of styrene and ortho-xylene, it would be more preferable to use as the organic compound in forming the first complex, an aromatic hydrocarbon such as benzene or toluene which may be readily separated from the ortho-xylene by simple distillation.

With the cuprous fiuoroborate and cuprous fluorophosphate-aromatic hydrocarbon first complexes, it is often found desirable to stabilize the activity of the complex. It has been found that in many instances when readily polymerizable vinyl aromatic hydrocarbons are brought into contact with these first complexes, a significant amount of the vinyl aromatic hydrocarbon is polymerized by the complex. To avoid such polymerization, the cuprous salt-aromatic hydrocarbon complex may be stabilized in activity by displacing a portion of the aromatic hydrocarbons from the complex with certain oxygen or sulfur containing compounds. In order to so stabilize the activity of the complex, the cuprous saltaromatic hydrocarbon complex is brought into contact with such oxygen or sulfur containing compounds being in molar excess of the amount of aromatic hydrocarbon in the complex. By such means, at least a portion, usually one or two moles, of the aromatic hydrocarbon is displaced from the cuprous salt-aromatic hydrocarbon complex and replaced by an equivalent molar amount of the oxygen or sulfur containing compound.

Among the oxygen and sulfur containing organic compounds useful for stabilizing the activity of the cuprous salt-aromatic hydrocarbon first complexes are the ethers, ketones, sulfones, disulfides, thiocthers, thioureas, nitro compounds, trihydrocarbonyl phosphines and the like. The useful ethers include acyclic ethers, alicyclic ethers, aryl ethers and alkyl aryl ethers. Several non-limiting examples of these compounds are such acyclic ethers as diethyl ether, di-n-propyl ether, di-n-butyl ether, di-isopropyl ether, di-isobutyl ether, di-tertbutyl ether, di-noctyl ether, and the like; such alicyclic, aryl and alkyl aryl ethers as tetrahydrofuran, furan, alkyl furans, alkyl tetrahydrofurans, 1,4-dioxane, 1,3-dioxane, alkyl derivatives of 1,4- and 1,3-dioxanes, alkyl substituted ethylene oxides, diphenyl ether, ditolyl ether, methyl phenyl ether, methyl tolyl ether and the like. The most useful ethers are the acyclic ethers of l to 10 carbon atoms in the alkyl radicals, furan, tetrahydrofuran, dioxanes, alkyl substituted ethylene oxides, alkyl furans, dioxanes and tetrahydrofurans of l to 10 carbon atoms in the alkyl radical, aryl and alkyl aryl ethers of no greater than 20 carbon atoms.

Ketones useful as stabilizing compounds include the alkyl ketones and the aromatic ketones. Several nonlimiting examples of such ketones include the alkyl ketones, including the diketones, such as dimethyl ketone, diethyl ketone, di-n-propyl ketone, di-n-butyl ketone, din-pentyl ketone, di-n-hexyl ketone, di-isopropyl ketone, methyl isopropyl ketone, di-isobutyl ketone, ethyl isobutyl ketone, butandione, 2,4-pentandione, 2,5-hexandione, and the like; the aromatic ketones such as acetophenone, phenyl alkyl ketones, benzophenone and alkyl benzophenones, benzoquinones and alkyl benzoquinones, and the like. Most useful are the alkyl ketones having 1 to 6 carbon atoms in the alkyl radical, phenyl alkyl ketones and benzoquinones containing no more than 12 carbon atoms.

The sulfones useful in the practice of the present invention include both the alkyl and aryl sulfones. Among the alkyl sulfones useful are such compounds as ethyl sulfone, propyl sulfone, methylethyl sulfone, methylbutyl sulfone, and other alkyl sulfones containing up to 6 carbon atoms in the alkyl radicals, the alkyl radicals being the same or different and being either straight chain or branched chain. The aryl sulfones include sulfolane and the alkyl sulfolanes, particularly the alkyl sulfolanes in which the alkyl radicals have 1 to 6 carbon atoms. The most useful of the sulfones are sulfolane and the methyl sulfolanes.

The disulfides which may be used include carbon disulfide and acyclic disulfides. Among the acyclic disulfides useful are such compounds as ethyl disulfide, propyl disulfide, and the like wherein the alkyl radicals contain 1 to 10 carbon atoms, either straight or branched chain and wherein the acyclic radicals are either the same or different. The preferred disulfides are those having 1 to 6 carbon atoms.

The thioethers useful in the present invention include both noncyclic and cyclic compounds. Among the noncyclic thioethers are such compounds as ethyl sulfide, propyl sulfide, butyl sulfide, methyl ethyl sulfide, methyl propyl sulfide, and the like wherein the alkyl radicals are the same or different, straight or branched-chain, and contain 1 to 10 carbon atoms. Preferably, these noncyclic thioethers contain 1 to 6 carbon atoms in the alkyl radi cals. The cyclic thioethers include thiophene, alkyl thiophenes in which the alkyl radicals are of l to 6 carbon atoms, tetrahydrothiophenes and alkyl tetrahydrothiophenes in which the alkyl radicals contain 1 to 6 carbon atoms. Preferred cyclic ethers are thiophene and alkyl thiophenes having no greater than 3 carbon atoms in the alkyl substituents.

Thioureas useful in the practice of the present invention include thiourea and the alkyl substituted thioureas. Usually, the thiourea will be one having no greater than 4 carbon atoms in each of the alkyl radicals. The preferred thiourea is thiourea itself.

The nitro compounds useful as stabilizing agents in the present invention include nitro alkyls and nitro aromatics. Among the nitro alkyls are such compounds as nitromethane, nitroethane, nitropropane, nitrobutane, and the like. The nitro aromatics include such compounds as nitrobenzene, dinitrobenzenes, nitrotoluenes and the like. Usually the nitro alkyls employed contain no greater than 12 carbon atoms in the alkyl group and the nitro aromatics contain no greater than 12 carbon atoms.

Trihydrocarbonylphosphines useful in the present invention include the trialkylphosphines, trialkylarylphosphines and triarylphosphines. Usually, the compounds of this group used in the practice of the present invention are those in which the total carbon atoms in the three hydrocarbonyl radicals is no greater than 24. The hydrocarbonyl radicals of such compounds may be the same or different in structure and carbon number. The preferred trihydrocarbonylphosphines are the triphenylphosphines and the methyl substituted derivatives thereof.

The amount of the oxygen or sulfur containing stabilizing compound employed may vary with the desires of the user. Preferably, however, it will be employed in molar excess to the amount of aromatic hydrocarbon in the first complex. In preparing the stabilized complex, a cuprous salt-aromatic hydrocarbon first complex is brought into contact with the oxygen or sulfur containing stabilizing compound with agitation. Temperature during this contacting and agitation period may vary widely ranging from sub-zero to as high as 100 C. and higher. Preferably, however, temperatures range from about 5 C. to 40 C.

In addition to the use of the above-described oxygen and sulfur containing stabilizing compounds to stabilize the polymerization activity of the cuprous salt containing first complexes prior to contact with vinyl aromatic hydrocarbons, it is preferred to further stabilize such first complex by the addition of olefin hydrocarbons thereto. This is accomplished either by the simultaneous addition of the oxygen or sulfur containing compound and an olefin as illustrated in Example I or by the addition of the olefin before or after addition of the oxygen or sulfur containing compound. The function of the olefin is believed to be that of reducing the heat generated by contact of the first complex with vinyl aromatic hydrocarbons which is based on the further belief that the amount of heat generated by removal and replacement of an alkyl aromatic hydrocarbon, such as toluene, from the first complex by vinyl aromatic hydrocarbons is greater than that generated by removal and replacement of an olefin by the vinyl aromatic hydrocarbon. The avoidance of heat is desired to prevent polymerization of vinyl aromatic hydrocarbons. The olefins useful in this preferred first complex include normal or iso-olefins of 2 to 20 carbon atoms and higher. The primary limitation on molecular weight of the olefins is that they should not be of such molecular weight as to result in formation of a solid first complex. Such molecular weight will vary according to the other hydrocarbons present and the particular oxygen or sulfur containing stabilizing compound present, if any. Usually, it is preferred to use the lower molecular weight olefins which are liquid or near liquid at ambient temperatures. Such olefins are readily removed from the system when desired without the use of significant heat. Among such preferred olefins are those having 4 to 8 carbon atoms, i.e., butenes, pentenes, hexenes, heptenes, and octenes.

The amount of olefin hydrocarbon used to aid in reducing the polymerization activity of the first complex may vary depending upon the circumstances. However, to insure a maximum utilization of olefin hydrocarbons in removing and replacing aromatic hydrocarbons, it is generally preferred to contact the aromatic-hydrocarbon containing complex with an amount of olefin in molar excess of the amount of aromatic hydrocarbon present in the first complex.

While the use of olefin hydrocarbons to further stabilize the first complex is above-described as used in conjuction with the use of an oxygen or sulfur containing stabilizing compound, it is not necessary that it be so used. The olefins may be employed to advantage without the use of such oxygen or sulfur containing compounds.

In general, it is unnecesary to stabilize the cuprous fiuorophosphate containing first complexes against polymerization activity. The above-discussed and described oxygen and sulfur containing stabilizing compounds often provide a second function with respect to the cuprous fluorophosphate-aromatic hydrocarbon complexes. As noted above, the cuprous fluorophosphate-aromatic hydrocarbon complexes may be solid at ordinary ambient temperatures and if used alone, usually require elevated temperatures. However, by the use of such compounds as the above-described oxygen and sulfur containing compounds as solvents, the cuprous fluorophosphate-aromatic hydrocarbon complexes may be utilized at ambient temperatures as well as stabilized in activity. In the preferred practice of the present invention with cuprous fluorophosphate-aromatic hydrocarbon complexes, one of the above-described solvents, particularly one of the sulfur containing compounds, i.e., sulfolane and its alkyl derivatives, is used as a solvent for the complex.

The amount of the first complex used in carrying out the separation of the vinyl aromatic hydrocarbons from the alkyl aromatic hydrocarbons in accordance with the process of the present invention may vary considerably. However, the amount most often used is such as to provide a mole ratio of the cuprous salt (OuBF or CuPF to the vinyl aromatic hydrocarbons in the mixture to be separated within the range of 0.25 :1 to 10:1. Preferably, however, the amount will be such as to provide a mole ratio of cuprous salt to available vinyl aromatic hydrocarbon of 0.33:1 to 4:1.

-It has been found particularly useful in carrying out the process of the present invention to use a noncomplexible hydrocarbon diluent or solvent as an aid to formation of the extract and rafiinate phases and/or for further extracting the extract phases formed to remove from such phase the hydrocarbons which are not complexed with the cuprous salt. In most instances, the noncomplexible hydrocarbon employed is an aliphatic hydrocarbon of 3 to 15 carbon atoms. Nonlimiting examples of such hydrocarbons are propane, n-butane, n-pentane, nhexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, isobutane isopentanes isoheptanes, isodecanes, isododecanes, isotridecane, cyclopentane, cyclohexane, methylcyclohexane, cycloheptane, and the like. Most often, the saturated aliphatic hydrocarbons are paraffinic hydrocarbons and may be straight-chain or branched-chain. Petroleum ether is a very practical and useful fraction for use in the present process. The most useful saturated aliphatic hydrocarbons are the parafiinic hydrocarbons of 4 to 7 carbon atoms per molecule.

The amount of noncomplexible hydrocarbon employed in the present process may vary considerably. The amount of such hydrocarbons used depends largely on the amount of alkyl aromatic hydrocarbons in the feed mixture and the degree of separation desired, etc. Usually, however, about 0.5 to volumes of noncomplexible hydrocarbon per volume of alkyl aromatic hydrocarbon in the feed mixture to be separated are used. Preferably, about 1 to 3 volumes of noncomplexible hydrocarbon will be used per volume of alkyl aromatic hydrocarbons in the feed mixture.

Conditions of temperature and pressure whereby the separations process of the present invention may be successfully practiced may vary rather widely. Most often, however, the process of the present invention will be practiced at temperatures within the range of 0 to 195 C., preferably, within the range of 25 to 150 C. The pressures most often employed for practicing the process of the present invention do not appear to be critical and may range from subatmospheric pressures to superatmospheric pressures. As a practical matter, it is usually desirable to operate at or near atmospheric pressure, the pressures ranging from as low as 50 mm. Hg to 250 p.s.i.g.

The present invention, as described herein, is useful for separation and recovery of vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons. The vinyl aromatic hydrocarbons which may be separated and recovered include such materials as styrene, tat-methyl styrene, fi-methyl styrene, vinyl toluene, divinyl benzene, vinyl naphthalene and the like. The alkyl aromatic hydrocarbons from which the vinyl aromatic hydrocarbons may be separated are exemplified by such hydrocarbons as ortho-, meta-, paraxylene, toluene, ethylbenzene, diethylbenzene, naphthalene, methylnaphthalenes and the like. In the preferred practice of the present invention, the vinyl aromatic-alkyl aromatic hydrocarbon mixture which is to be separated in accordance with the present invention is one containing artlamatic hydrocarbons of 8 to 9 carbon atoms per molecu e.

In the preferred mode of recovering the vinyl aromatic hydrocarbons from the extract phase resulting from contact of the feed mixture containing vinyl aromatic and alkyl aromatic hydrocarbons with the first complex, the extract phase is intimately mixed with an olefin hydrocarbon. The amount of olefin hydrocarbon is at least a molar equivalent of the amount of vinyl aromatic hydrocarbon in the extract phase. Preferably, the olefin hydrocarbon is used in a molar excess over the amount of vinyl aromatic hydrocarbons in the extract. For example, it is very useful to employ 1.1 to 2.5 moles of olefin hydrocarbons per mole of vinyl aromatic hydrocarbons in the extract phase. The olefins which may be used in the recovery of the vinyl aromatic hydrocarbons from the extract phase include those of 2 to carbon atoms and higher. These olefins may be terminally or internally un saturated, branched or straight chain, cyclic or noncyclic. In the preferred practice, the olefin hydrocarbons are those having 2 to 10 carbon atoms. Particularly preferred are the pentenes, hexenes and heptenes. In choosing the olefin hydrocarbon to use in displacing vinyl aromatic hydrocarbons from the extract phase, care should be exercised to avoid using one which is itself difiicultly separable from components of the system. As hereinabove mentioned, the olefin hydrocarbon containing extract phase resulting after displacement of vinyl aromatic hy- 12 drocarbons from the extract phase may be used as at least a portion of the first complex by which the vinyl aromatic hydrocarbons are separated from the alkyl aromatic hydrocarbons.

What is claimed is:

1. A process for the separation and recovery of vinyl aromatic hydrocarbons from admixture with alkyl aro matic hydrocarbons comprising contacting a mixture of said vinyl aromatic hydrocarbons and said alkyl aromatic hydrocarbons with a first complex which comprises a cuprous salt selected from the group consisting of cuprous fluoroborate and cuprous fiuorophosphate and a hydrocarbon selected from the group consisting of olefins, aromatic hydrocarbons and mixtures of olefin and aromatic hydrocarbons, said aromatic hydrocarbons being other than vinyl aromatic hydrocarbons, thereby forming a first extract phase and a first raffinate phase, separating said first extract phase and said first raffinate phase, and recovering from said first extract phase a hydrocarbon fraction substantially richer in vinyl aromatic hydrocarbons than the original mixture.

2. The process of claim 1 wherein the cuprous salt is cuprous fluoroborate.

3. The process of claim 2 wherein the first complex comprises cuprous fluoroborate and an aromatic hydrocarbon.

4. The process of claim 3 wherein the aromatic hydrocarbon is selected from the group consisting of benzene, naphthalene, partially hydrogenated naphthalenes, the alkyl substituted derivatives of these wherein the alkyl substituents have no more than 4 carbon atoms per substituent, and mixtures of these.

5. The process of claim 4 wherein the aromatic hydrocarbon is toluene.

6. The process of claim 2 wherein said first complex is stabilized with a compound selected from the group consisting of ethers, ketones, sulfones, disulfides, thioethers, thioureas, nitro compounds, trihydrocarbonyl phosphines and combinations thereof.

7. The process of claim 6 wherein said compound is an ether selected from the group consisting of 1) acyclic ethers of 1 to 10 carbon atoms in the alkyl radicals, (2) furan, (3) tetrahydrofuran, (4) dioxanes, (5) alkyl substituted ethylene oxides, (6) alkyl furans, dioxanes and tetrahydrofurans of 1 to 10 carbon atoms in the alkyl radical, and (7) aryl and alkyl aryl ethers of no greater than 20 carbon atoms.

8. The process of claim 6 wherein said compound is a ketone selected from the group consisting of alkyl ketones and alkyl diketones having 1 to 6 carbon atoms in the alkyl radical, phenyl alkyl ketones and benzoquinones containing no more than 12 carbon atoms.

9. The process of claim 6 wherein said compound is a sulfone selected from the group consisting of sulfolane, alkyl sulfolanes in which the alkyl radicals have 1 t0 6 carbon atoms and alkyl sulfones containing no greater than 6 carbon atoms in the alkyl radicals.

10. The process of claim 6 wherein said compound is a disulfide selected from the group consisting of carbon disulfide and acyclic disulfides containing 1 to 10 carbon atoms.

11. The process of claim 6 wherein said compound is a thioether selected from the group consisting of noncyclic thioethers of 1 to 10 carbon atoms, thiophene, tetrahydrothiophene, and the alkyl substituted thiophenes and tetrahydrothiophenes in which the alkyl radicals contain 1 to 6 carbon atoms.

12. The process of claim 6 wherein said compound is a thiourea selected from the group consisting of thiourea and the alkyl substituted thioureas having no greater than 4 carbon atoms in each of the alkyl radicals.

13. The process of claim 6 wherein said compound is a nitro compound selected from the group consisting of nitro alkyls and nitro aromatics containing no greater than 12 carbon atoms.

14. The process of claim 1 wherein said hydrocarbon fraction substantially richer in vinyl aromatic hydrocarbons is recovered from said first extract phase by contacting said first extract phase with olefin hydrocarbons, the amount of olefin hydrocarbon being at least a molar equivalent of the amount of vinyl aromatic hydrocarbon in said extract phase.

15. The process of claim 14 wherein said olefin hydrocarbon is one having 2 to 15 carbon atoms.

16. The process of claim 1 wherein said mixture is contacted with said first complex at a temperature within the range of to 195 C.

17. The process of claim 1 wherein said mixture of vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbons are contacted with said first complex in the pres ence of a noncomplexible hydrocarbon.

18. The process of claim 17 wherein said noncomplexible hydrocarbon is an aliphatic hydrocarbon of 3 to 15 carbon atoms.

19. The process of claim 1 wherein said first complex is present in an amount such as to provide a mole ratio of cuprous salt to vinyl aromatic hydrocarbons in the mixture to be separated within the range of 0.25:1 to :1.

20. A process for the separation and recovery of vinyl aromatic hydrocarbons from admixture with alkyl aromatic hydrocarbons which comprises introducing a mixture of such hydrocarbons into a first extraction column between the ends thereof, concurrently introducing near the top of said extraction column a first complex comprising a cuprous salt selected from the group consisting of cuprous fluoroborate and cuprous fluorophosphate and a hydrocarbon selected from the group consisting of olefins, aromatic hydrocarbons and mixtures of olefin and aromatic hydrocarbons, said aromatic hydrocarbons being other than vinyl aromatic hydrocarbons, concurrently introducing into said extraction column near the bottom thereof a noncomplexible hydrocarbon, removing overhead from said first extraction column a first rafiinate containing a ratio of alkyl aromatic hydrocarbons to vinyl aromatic hydrocarbons substantially greater than that in the original mixture, removing from the bottom of said extraction column a first extract phase, introducing said first extract phase into a second extraction column above the midpoint thereof, concurrently introducing an olefin hydrocarbon of a molecular weight different from that of the vinyl aromatic hydrocarbons in said first extract phase and in a quantity which is at least in molar equivalent to the vinyl aromatic hydrocarbons in said first extract phase, and concurrently introducing noncomplexible hydrocarbons into said second extraction column, both said olefin hydrocarbons and said noncomplexible hydrocarbons being introduced near the bottom of said second extraction column, removing from the bottom of said second extraction column a second extract phase at least a portion of which is recycled to said first extraction column as at least a portion of said first complex, removing overhead from said second extraction column a second raffinate containing a ratio of vinyl aromatic hydrocarbon to alkyl aromatic hydrocarbons substantially greater than that in said original mixture.

References Cited UNITED STATES PATENTS 2,953,589 9/1960 McCaulay 260-674 DELBERT E. GANTZ, Primary Examiner C. R. DAVIS, Assistant Examiner US. Cl. X.R. 260669 

